Astatic material



Aug. 18, 1953 s. A. SIMON ET AL 2,649,143

ASTATIC MATERIAL Filed June 4, 1949 /5 Tlcll.

Patented Aug. 18, 1953 UNITED STATES PATENT OFFICE ASTATIC MATERIAL of Massachusetts Application June 4, 1949, Serial No. 97,301 In Canada June 4, 1948 4 Claims. (Cl. 1515-182) Abstract Dielectric materials, particularly plastics gellerate electrostatic charges when rubbed With various fabrics commonly used for clothing. Such electrostatic plastic materials are mechanically suitable for upholstery fabrics and other purposes, but generation of electrostatic charges have produced uncomfortable shocks to users of the material. This has been especially aggravated with automobile seat covers. The invention provides a treatment for such materials which eliminates or materially reduces the prollerty of shocking users. The material is dipped in a dilute dispersion of any of a class of chemicals Which is deiined and illustrated herein.

This application is a continuation-in-part of our application Ser. No. 32,520, filed June llI 1948, now Patent No. 2,628,176.

This invention relates to the treatment of Clelectric materials to prevent them from inducing or accumulating charges of static electricity. One aspect or" the invention is concerned with astatic dielectric materials used for covering seats, particularly vehicle seats and especially in automobiles. In general the objects of the invention include the provision of improved astatic dielectric material, the devising of an improved process of antistatic treatment of dielectric material to render it astatic and the provision of improved seats, particularly in vehicles which seats do not generate nor accumulate objectionable electrostatic charges, and thus do not shock passengers. It is particularly an object to provide effective antistatic treatment of chemically inert and physically smooth and slippery dielectric materials.

As used herein, the term astatic denotes absence of the property or ability to generate, induce or accumulate objectionable electrostatic charges, and the term antistatic pertains to reducing or eliminating the property or ability to generate, induce or accumulate electrostatic charges. That is, an antistatic agent tends to produce an astatic result.

As used herein, the term plastic has a meaning more restricted than the indenite sense in which it is popularly used. As used herein, plastic designates a non-cellulosic high polymer (usually but not necessarily organic) of synthetic origin (as opposed to being found in nature) and either molded into a solid or capable of being so molded. This definition includes, for example7 saran and other vinyl resins; methacrylate resins; polyethylene; nylon; poly-tetra-.luoroethylene and others,

It is known that various plastics (which incidentally are non-conductors of electricity and called dielectrics) have the inherent property of generating static charges of electricity when rubbed with various other dielectric materials, such as Wool, silk, cotton, fur and the like. Plastic articles in everyday use develop electrostatic charges, probably as a result or unavoidable friction, and these electrostatic charges have many undesirable results which include the production of dangerous sparks and uncomfortable shocks to users of the materials.

Upholstered seats are frequently covered with material intended to be durable, Water resistant and easily cleanable. In recent years much effort has been directed to the provision of seat cover materials and textiles which have the desirable properties of strength, iiexibility, softness, comfortable feel, great durability under extreme abuse and high resistance to chemical action. Many synthetic plastics have been proposed. An outstanding material developed by this eiort is Saran. We understand this to be technically either polyvinyldene chloride or a copolymer of vinylidene chloride with vinyl chloride and/or acrylonitrile, in any case suitably combined With various plasticizers to impart the desired physical properties to the polymer. Such material and the method of making it are well known. It is commonly extruded into laments Which are Woven into textiles, or the material may be formed as sheets. The commercial saran has a very smooth surface and is extremely inert chemically, making it highly resistant to soiling and easily cleanable, and this combined with its particular physical properties makes it an excellent seat covering material, except for its inherent undesirable electrostatic properties. Another material of similar durability and mechanical properties is polyethylene.

Rubbing saran or polyethylene lightly with common textile materials used for clothing, e. g. cotton or wool, generates particularly heavy and objectionable electrostatic charges. While the generation, transmission, induction and accumulation of electrostatic charges, and the exact causes of these phenomena are imperfectly understood, it is a demonstrated fact that when the clothing of a person is brushed over a seat covered With these various dielectric materials a heavy electrical charge is produced on the seat cover and a heavy charge, presumably equal and opposite, is produced on the person. Thereafter if the person closely approaches a grounded conductor, such as a Water pipe, or a conducting mass of sucient electrical capacity which is either not charged or is carrying a charge of pposite polarity or sign (e. g. an isolated car body), a spark may pass between the person and this other object. The accompanying shock is sta-rtling, uncomfortable, frequently painful, and the spark may even be dangerous.

The phenomenon of static discharge or spark,- ing due to seat covers is especially aggravated in the case of passengers in automobiles. We believe this inay be due either tov excessive friction caused by passengers sliding across the seat covers in getting into or out of cars, or to the excessive friction caused by passengersy clothing unavoidably sliding over the backs of seats in the course of uneven motion of the vehicle, 0rto both of these causes, combined with the condition that the passenger is normally held by the seat and insulating floor covering out of electrical contact with the large metallic masses of the car such as frame and body, which have substantial electrical capacity, and which may either be isolated or insulated in space by the tires, if dry, or may be electrically connected to the ground if the tires are wet. There is also some evidence that static is caused by simple operation of the vehicle over a smooth road. This may conceivably be due to wind friction or tire friction. In any case, after a brief period of operation of a vehicle equipped with seats covered with various dielectric materials, especially Saran or polyethylene, frequently a very heavy charge may be discharge or conducted away from the passenger through a spark whenever the passenger becomes connected to the high capacity metallic masses in the body of the car, as by touching a door handle, or when the passenger steps out on the ground.

It has been proposed to render various material astatic by coating with antistatic agents or possibly chemically combining antistatic agents with dielectric materials. However, in the instances which have come to our attention, the proposed treatments have not been completely successful for one or a number of reasons. For example, some materials such as saran and polytetra-fluoro-ethylene are so smooth and so chemically inert that it has been regarded as irnpossible to cause any materials either to combine with them or adhere to them. Some proposed antistatic coatings for other materials so change the properties of the material or its surface as to make it undesirable for other reasons., although it might have astatic properties. Also, although materials are known which for a time impart some degree of astatic character to some dielectrics, such astatic properties are not sufciently lasting to be satisfactory, for example, either because the antistatic materials readily wash olf 0r are otherwise removed in normal use, or because the astatic property rapidly diminishes and disappears. Other proposed antistatic agents are hygroscopic and undesirably attract water to the surfaces to which they are applied, and this prevents their being useful in many instances.

We have discovered that the materials in a certain group or class, which we designate by the coined word etymols, have antistatic properties, and that they combine with various dielectric materials (not necessarily in the chemical sense) or adhere to such dielectrics, particularly those plastics which are the subject of this invention, and when so combined or adhered render the dielectrics astatic.

The etymols are defined as long chain fatty g5 4 acid partial esters (including the poly-oxy-alkylene ethers of such esters) of the following:

A. Those aliphatic poly-hydroxy alcohols having from two to six carbon atoms and from two to six hydroxyl groups;

B. Monomeric cyclic ethers of such poly-hydroxy alcohols;

C; Polymeric ethers having at least two hydroxyl groups and which may be considered condensation products of such poly-hydroxy alcohols.

The etymols include, for example, the following materialsA arrangedv as sub-groups of A, B, and C above:

a. Glyccryl esters such as glyceryl monostearate, mono-oleate, etc. and poly-oxyethylene propylene glycol mono-stearato,

b. Long chain fatty acid partial esters of the hexitans (that is esters of monomeric cyclic ethers of hexitol) and hydroxypoly-alkylene ethers thereof such as Sorbitan mono-laurate, and sorbitan monolaurate poly-oXy-ethylene other,

c. Polyethylene glycol esters, such as polyethylene glycol mono stearate, monooleate, etc., and the polyethylene-glycol ether of poly-propylene-glycol mono-stearate.

We have discovered that the etymols are particularly effective in imparting astatic properties to plastics, that the etymols surprisingly combine with or adhere to various inert and smooth or slippery plastics (for example Saran and polyethylene) and together with such materials forni astatic articles or substances. We have also discovered that certain of these etymols, although readily dispersible in water, nevertheless when placed upon certain plastics impart a durable astatic character thereto, which resists scrubbing and washing.

Based on these discoveries, it is an object of our invention to render astatic normally electrostatic plastics and thus to provide materials with desirable mechanical and physical properties for many uses for which they were formerly unsuitable because of undesirable electrostatic properties.

Also based on these discoveries, it is among the objects of our invention to provide improved seat cover material and improved seats which do not shock people using them, and particularly to prov-ide improved automobiles having seats covered with saran which does not shock passengers.

Since our invention is particularly useful when applied to material used for upholstery or seat covers, especially those used in automobiles and other vehicles we shall describe our invention, for example only, as used with such articles and materials.

In the accompanying drawings:

Fig. 1 is an elevation of an automobile embodying our invention;

Fig. 2 is 'an enlarged perspective view of a portion of a seat embodying our invention;

Fig. 3 is an enlarged elevation partly in section of a portion of a seat showing our improved seat facing material; and

Fig. 4 'is a chart on which are `plotted the preferred concentrations of the dispersions of material used to impart astatic properties to the seat facing material.

In Figs. l and 2, I0 represents a conventional automobile normally held out of electrical contact with the ground by tires Il and having large masses of metal such as doors l2, body panels I4 and top I6 which enclose a passenger compartment I8 having one or more upholstered seats and an insulating floor covering 22, The seat 20 includes an upholstered seat proper 2li and upholstered back rest 26. As described, the construction and arrangement are well known and their particular features `are matters of choice.

In accordance with our invention we cover the operative or passenger supporting faces of the seat vand back rest with a suitable plastic, Saran or polyethylene for example, either in the form of a sheet (that is a thick lm) or preferably in the form of a closely woven but pervious textile cloth 28. One we have found suitable is ya fabric woven as closely as is practical from extruded single filaments of saran, of about ten to twelve mils diameter. This sheet or cloth may be applied to the seat and back in any suitable or conventional manner, either as the permanent facing when the seat is constructed, or as a removable covering or slip cover.

At any convenient time befo-re the car is used, and preferably after the plastic is woven but before the cloth is made into seat covers, we dip, brush or spray the cloth with a dilute dispersion or solution of a suitable etymol in a volatile carrier such as water, alcohol, or carbon tetrachloride and then dry the cloth. We prefer the water dispersion. We have found surprisingly that the etymols adhere to, combine with (not necessarily in the chemical sense) or otherwise cooperate with inert plastics such as saran to provide a durable astatic combination. This combination resists both dry abrasion (incident to use) and with some etymols, repeated scrubbing with a stiff bristle brush and water or soap solution (incident to cleaning). These results and these properties are contrary to what is to be expected from the individual. properties of the plastic and the etymols. Thus saran is known for its very smooth surface and high degree of chemical inertness. Consequently heretofore it has been considered impossible to combine anything with Saran or to make anything adhere to it. Also while many of the etymols are regarded as insoluble in water, they are readily dispersible. Consequently it is contrary to the known properties both of the plastics and the etymols that they form a combination and that this combination resists separation by active scrubbing.

Moreover very small quantities of the etymols produce an astatic combination with the plastics, even with saran. W e have found that a concentration of 1/870 of sorbitan monolaurate, for example, in the treating dispersion produces a noticeable astatic effect, and that the saran can be rendered completely Iastatic by concentrations of less than l The tabulation below shows the range of concentrations o-f a water dispersion of sorbitan mono-laurate which we have found effective to render the saran astatic. A -closely woven fabric of saran monola-ments was dipped in dispersions of the concentrations indicated, and :after drying was rubbed briskly with a woolen cloth. The sara-n was then brought near a sensitivc electroscope.

In the tabulation below the numerical values of needle deflection Iare approximately proportional to the voltage induced on a very sensitive deiiecting needle electroscope. The deilection 5 represents the highest induced voltage which we have found to be permissible. That is a piece of Saran cloth, charged to a voltage of 5 as shown by this electroscope, will discharge so as to produce a noticeable shock to Ia person connected with it. A deection of greater than 5 indicates that the shock will be uncomfortable and objectionable. A deiiection of less than 5 will not produce noticeable or objectional shock.

Needle Deilection Percent Concentration of Antistatic Dispersion As Will be seen from the tabulation a dispersion of 1/8% markedlyreduces the charge that can be induced on the plastic, and may be said to represent the minimum operative concentration of the particular etymol sorbitan monolaurate when used with saran, while a concentration of 1A1% reduces the charge to a value well within the acceptable range and 1/2% elminiates static completely.

When applied to textile fabrics woven from single filaments of labout ten or twelve mils diameter, the above dispersions, after drying, increase the weight of the fabric by about one-third of the percentage of the concentration of the dispersion. Thus the treatment with a dispersion of l/gf; increases the weight of the fabric about 1/e%.

We do not known the exact nature of the resulting plastic treated with the etymols. Apparently evaporation of the carrier from dispersions of low concentration does not leave a simple lm or coating when can be identified and described as such. And as yet we have no positive evidence that there is any chemical combination between the plastic and etymol. The only way we can dene the treated combination of plastic and an etymol is to say that this combination has electrostatic properties substantially identical with the plastic which has been covered with a dispersion of the etymol.

As indicated by the tabulation, concentrations of sorbitan mono-laurate greater than 1/2 satisfactorily eliminate static, but we have found that concentrations above about 2% give the saran fabric an objectionable feel. Therefore, we use concentrations within the range 1/8% to 2% and prefer to use between l/4% to 1%.

Example I A Saran cloth finely woven from single laments having a diameter of 10 to 12 mils was dipped in a 1% dispersion in water of sorbitan mono-laurate and dried. The resulting treated cloth showed a relative static charge of 2 by the electroscope when vigorously rubbed with woolen cloth. A seat cover of this material was applied to the seat of an otherwise conventional automobile which was operated with two passengers under conditions known to develop objectionable static in untreated seats. The seat developed no objectionable static in operation.

Ezvample I I A saran cloth nely woven from single laments having a diameter of l0 to l2 mils was dipped in a 1% dispersion in water of sorbitan mono-laurate and dried. The resulting treated cloth showed no static by the electroscope when vigorously rubbed with woolen cloth. The fabric:A

was made into a seat cover and applied to the seat of an otherwise conventional automobile, which was operated with two passengers under conditions known to develop objectionable static in untreated Saran seats. The seat developed no static in operation. The seat cover was scrubbed vigorously-with soap solution and a stiff brush. After four repeated scrubbings the seat developed no static in operation and samples showed no 'charge on the electroscope when briskly rubbed with woolen cloth.

Example III A saran cloth finely woven from single laments having a diameter of to 12 mils was dipped in a 1% dispersion in water of the reaction product of sorbitan mono-stearato with 20 mols ethylene oxide. The resulting treated cloth showed no static by the electroscope when vigorously rubbed with woolen cloth. A seat cover of this fabric was applied to a conventional automobile which was operated with two passengers under conditions known to develop objectionable static in untreated seats. The seats developed no objectionable static in operation. The seat cover was scrubbed vigorously with soap solution and a stiff brush. Thereafter the seat developed observable amounts of static, and after a second scrubbing objectionable amounts of static developed.

The class of etymols includes a large number of substances which are closely related in chemical structure and antistatic properties. For example, the aliphatic poly-hydroxy alcohols from which the partial esters and ethers thereof can be derived include ethylene glycol; diand triethylene glycol; glycerol and polyglycerols, pentaerythritol; pentitols; hexitols and the monomeric cyclic others thereof; cyclitols such as inositol; oligosaccharides such as glucose, sucrose and lactose; the glycol and lower polyglycol ethers of the above named poly-hydroxy alcohols. The esters of the mixed monomeric cyclic ethers of the hexitols (such as sorbitans and sorbides, inannitans and mannides) and the poly-oxy-alltylene ethers thereof are suitable etymols. The hydroxy-poly-oxy-ethylene e'thers of these esters can be prepared by reacting the partial ester with a preformed polyethylene glycol or with 10 to 30 mols of ethylene oxide. Such reaction products are known in the literature and are named, for example, reaction products of sorbitan monolaurate with 20 mols ethylene oxide, or more simply sorbitan mono-laurate poly-oxyethylene ether. Specific etymols which We have found suitable antistatics are:

Diethylene glycol mono-laurate Diethylene glycol mono-stearato Ethylene glycol mono-laurate Ethylene glycol mono-myristate Ethylene glycol mono-ricinoleate Glycerol mono-laurate Glycerol mono-myristate Glycerol mono-oleate Glycerol mono-ricinoleate Mannitan di-laurate poly-oxy-ethylene ether Mannitan mono-oleate Mannitan mono-oleate poly-oxy-ethylene ether Mono-penta-erythritol ester of soy oil fatty acids Penta-erythritol mono-oleate Penta-erythritol mono-stearate Polyethylene glycol mono-laurate Polyethylene glycol mono-myristate Polyethylene glycol mono-oleate Polyethylene glycol mono-ricinoleate Polyethylene glycol mono-stearate Poly-oxy-ethylene propylene glycol mono-stearate Propylene glycol mono-myristate Propylene glycol mono-oleate Propylene glycol mono-stearato Propylene glycol mono-ricinoleate Sorbitan mono-laurate sorbitan mono-laurate poly-oxy-ethylene ether sorbitan mono-naphthenate Sorbitan mono-oleate sorbitan mono-oleate poly-oxy-e'thylene ether Sorbitan mono-palmitate Sorbitan mono-palmitate ether sorbitan mono-stearato Sorbitan mono-stearate poly-oxy-ethylene ether Sorbi'tan tri-oleate Sorbitan tri-oleate poly-oxy-ethylene ether While the etymols generally impart astatic qualities to the plastics, there are measurable differences in the intensity and durability under various conditions of these qualities which have been effected by the various specific etymols.

For example, the degree of reduction of static for a given concentration of applied dispersion varies from etymol to etymol. Thus the concentration of the etymol dispersion originally applied varies. Also a large number of etymols originally impart a satisfactory or equal degree of astatic property to the plastic, but there are variations in the life of the astatic property when the plastic is stored, and in the durability of the astatic property is use (resistance to friction) and in the resistance of the astatic property to cleaning or scrubbing. There is also a variation from etymol to etymol of the astatic properties of the plastic at low temperature such as 20 F.

However, the nature, extent and durability of the astatic property achieved by any specific etymol appears to be independent of the plastic to which the etymol is applied, at least as far as can be detected in ordinary conditions of use. Thus sorbitan mono-laurate applied at a given concentration of dispersion for example, appears to impart substantially equal astatic properties to saran, polyethylene, various vinyl resins, methaicrylate resins, nylon, poly-tetra-fluoro-ethylene, e c.

Of the etymols named, we prefer polyoxyethylene propylene glycol monostearate because of its ready availability and easy application, and because it gives satisfactory astatic properties even at low temperatures, which have long shelf life and are resistant to friction, and to washing. Other particularly effective etymols are poly- Oxy-ethylene propylene glycol mono-stearato, glyceryl mono-ricinoleate, polyethylene glycol mono-oleate, sorbitan mono-laurate, sorbitan mono-stearate poly-oxy-ethylene ether and sorbitan tri-oleate poly-oxy-ethylene ether, pentaerithritol mono-oleate.

Also, we may use blends or mixtures of the etymols to combine the good properties of several. Thus we may combine for example, an etymol giving particularly good astatic properties at low temperature with one having exceptional resistance to washing to obtain an antistatic agent having both properties.

It will be understood that our invention is not limited to the illustrations of the foregoing explanation, but includes what is dened within the scope of the appended claims.

We claim as our invention:

1. In a seat, the combination of means for suppoly-oXy-ethylene porting a person and a cover of a non-cellulosic synthetic long-chain polymer for the supporting means, the cover being treated and covered with an antistatic agent selected from the class consisting of long chain fatty acid partial esters and poly-oxy-alkylene ethers of long chain fatty acid partial esters of a compound selected from the group consisting of aliphatic poly-hydroxy alcohols having from two to siX carbon atoms and from two to six hydroxyl groups, monomeric cyclic ethers of aliphatic poly-hydroxy alcohols having from two to six carbon atoms and from two to six hydroxyl groups, and polymeric ethers having at least two hydroxyl groups which are condensation products of aliphatic poly-hydroxy alcohols having from two to six carbon atoms and from two to six hydroxyl groups; whereby it is substantially incapable of generating, inducing, and accumulating objectionable electrostatic charges; the antistatic agent being resistant to separation from the cover by scrubbing in water.

2. In a seat, the combination of means for supporting a person and a cover for the supporting means woven from laments of a non-cellulosic synthetic long-chain polymer, the cover for the supporting means being treated and covered with an amount within the range of from about 1/4% to about 2/3%, based on the weight of the cover, of an antistatic agent selected from the class consisting of long chain fatty acid partial esters and poly-oxy-alkylene ethers of long chain fatty acid partial esters of a compound selected from 'the group consisting of aliphatic poly-hydroxy a1- cohols having from two to six carbon atoms and from two to six hydroxyl groups, monomeric cyclic ethers of aliphatic poly-hydroxy alcohols having from two to six carbon atoms and from two to six hydroxyl groups, and polymeric ethers having at least two hydroxyl groups which are condensation products of aliphatic poly-hydroxy alcohols having from two to six carbon atoms and from two to six hydroxyl groups; whereby it is substantially incapable of generating, inducing, and accumulating objectionable electrostatic charges; the antistatic agent being resistant to separation from the cover by scrubbing in water.

3. In a seat, the combination of means for supporting a person and a cover of a noncellulosic synthetic long-chain polymer for the supporting means, the cover for the supporting means being treated and covered with an aqueous dispersion of glycerol monolaurate; whereby the cover is substantially incapable of generating, inducing and accumulating objectionable electrostatic charges, the glycerol monolaurate being resistant to separation from the cover by scrubbing in water.

4. In a seat, the combination of means for supporting a person and a cover of a noncellulosic synthetic long-chain polymer for the supporting means, the cover for the supporting means being treated and covered with an aqueous dispersion of poly-oxyethylene propylene glycol monostearate; whereby the cover is substantially incapable of generating, inducing and accumulating objectionable electrostatic charges, the poly-oxyethylene propylene glycol monostearate being resistant to separation from the cover by scrubbing in water.

SIMON A. SIMON.

Atlas, Surface Active Agents, Atlas Power Co., 1948, pages 67-68, between pages 26 and 27.

Atlas, Surface Active Agents, published by published by and Table 1 Atlas Powder Company, June 1945, pages 2 and 3. 

